As an image display device substitutable for liquid crystal device (LCD), image display devices (displays) with the use of technology such as an electrophoresis method, an electrochromic method, a thermal method, dichroic-particles-rotary method are proposed.
As for these image display device, it is conceivable as inexpensive visual display device of the next generation from a merit having wide field of vision close to normal printed matter, having smaller consumption power, and having a memory capability in comparison with LCD, spreading out to a display for portable device, and an electronic paper is expected.
Recently, electrophoresis method is proposed that micro-encapsulate dispersion liquid made up with dispersion particles and coloration solution and dispose the liquid between faced substrates. However, in the electrophoresis method, there is a problem that a response speed is slow by the reason of viscosity resistance because the particles migrate among the electrophoresis solution. Further, there is a problem of lacking imaging repetition stability, because particles with high specific gravity of titanium oxide is scattered within solution of low specific gravity, it is easy to subside, difficult to maintain a stability of dispersion state. Even in the case of micro-encapsulation, cell size is diminished to a microcapsule level in order to make it hard to appear, however, an essential problem was not overcome at all.
Besides the electrophoresis method using behavior in the solution as above-mentioned, recently, a dry visual display system (device) for displaying reversible images wherein two kinds of particles which are different in color and charging polarity are placed between a pair of substrates, and an electric field is given to fly and fix the particles to the substrates in different direction without using solution is proposed. [The Imaging Society of Japan “Japan Hardcopy'99” (Jul. 21-23, 1999) Transaction Pages 249-252, etc.]
Movement mechanism of such a dry visual display device employs as display device with material mixed two kinds in color and charging polarity are an electrode substrate and apply the voltage to generate an electric field between electrode substrates for flying the charged particle which have different polarity to a different direction.
In this system (device), an attracting force caused by Coulomb force between particles each other, an electric imaging force with an electrode plate, an intermolecular force, further, a solution cross-linking force, gravities and so on are considered as the force applied on the particles. The flight of the particles starts when the force working on the particles by an electric field exceeds those total forces. Then, each particles form patterns and contrasts by differences of the hue resulting in making viewers recognize the patterns. The higher the contrast, the better the visibility of the displaying means.
Further, this system has advantages that the migration resistance of the particles is small, and that the response speed is fast because it is not electrophoresis method but dry visual display system.
However, with such a dry visual display device, there were the problems as the following:    (1) The structure becomes complicated because a charge transport layer and a charge generation layer are disposed.    (2) It is difficult to constantly dissipate charges from electroconductive particles, therefore two kinds of particles electrostatically aggregate while repeating display thereby not respond to electrostatic field, resulting in short longevity and lack of stability.    (3) Colors become indistinct and lack luminance because the system utilizes the reflected-light from the particles for the display, resulting in the degradation of a vivid image display.    (4) Because a generation of strong electric field is necessary in an occasion of driving, and because a design of the electric circuit that can bear the strong electric field, general purpose electronic materials are not employable.